1. Field of the Invention
The present invention relates to a position detecting apparatus for detecting the position of an underwater moving body, which is applicable to a supersonic crack detecting system for an atomic reactor vessel (UT machine), and to metering of coordinates of tube header holes of an atomic reactor vessel, metering of center positions of key-slots and metering of sizes for use in a process of building a bridge by omitting temporary assembly.
2. Description of the Prior Art
An outline of an apparatus of the above-mentioned type in the prior art is shown in FIG. 7. Supersonic crack detection can be carried out by inspecting a structure 2 (of steel or the like) submerged in water 1 as shown in this figure. This inspection is carried out by a movable truck 40 loaded with a supersonic sensor 3 which is moved up and down by the rotation of a rod 41. The rod 41 is rotationally driven by a drive motor 43 disposed on a position detecting and moving mechanism 42. Inspection data of the structure 2 obtained from the supersonic sensor 3 as a result of movement of this movable truck 40 are sent to a control unit 45 along with position data for the movable truck 40 measured by a position detector section 44 loaded on the movable truck 40. The inspection data is evaluated by comparing it with the position data. It is to be noted the inspection is controlled by the control unit 45. While the illustrated example utilizes only a single rod 41, a plurality of rods 41 can be employed so as to simultaneously carry out various inspections. In addition, different measuring sensors can be mounted on the movable truck 40 in place of the supersonic sensor 3 to perform various measurements other than those for supersonic crack detection.
However, this prior art inspection apparatus is affected by the following problems:
(1) The position detecting and moving mechanism 42 for moving and controlling the movable truck 40 loaded with the supersonic sensor 3 is relatively large, and requires a significant amount of time and labor to prepare it for the inspection. PA0 (2) The precision in detecting the position of the movable truck 40 is poor due to the size of the detecting and moving mechanism 42 and the number of the rods 41. PA0 (3) The movable truck has little freedom of movement during the inspection due to its connection to the rods 41. Therefore it is necessary to change the positions of the rods in order to change the position of the movable truck 40. This results in a poor working efficiency.